A) 1 and 3 are meso isomers. B) 2 and 4 are not identical as 2 is R,R and 4 is S,S C) They are all not identical D) 1 and 2 are not enantiomers, thery are diasteriomers. Solution A) 1 and 3 are meso isomers. B) 2 and 4 are not identical as 2 is R,R and 4 is S,S C) They are all not identical D) 1 and 2 are not enantiomers, thery are diasteriomers..